Compatibility of the Vinylidene Ligand and Perfluorophenoxide

This study demonstrates the stability of the Ru-vinylidene moiety toward installation of a perfluorophenoxide ligand. The room-temperature reaction of RuCl(dcypb)(μ-Cl)3Ru(dcypb)(N2) (3) with TlOC6F5 and excess tert-butylacetylene yields mononuclear Ru(OC6F5)2(dcypb)(CCHBut) (6, dcypb = 1,4-bis(dicyclohexylphosphino)butane). Intermediates en route to 6 are the face-bridged dimers RuCl(dcypb)(μ-Cl)3Ru(dcypb)(CCHBut) (4a) and [{Ru(dcypb)(CCHBut)}2(μ-Cl)3]OC6F5 (5·OC6F5):  the cation in the latter was characterized as its PF6 salt (reaction halting at 5·PF6 on use of TlPF6 in place of TlOC6F5). Edge-bridged, dicationic [{RuCl(dcypb)(CCHBut)}2(μ-Cl)2](OC6F5)2 (8) is also a probable intermediate in this reaction pathway:  although not observed directly, the dication was isolated in low yields as its BArf4 salt, on reaction of 5·PF6 with NaBArf4 (BArf4- = [B{C6H3(CF3)2-3,5}4]-). A minor byproduct in the synthesis of 6 is acetylide Tl[{Ru(C⋮CBut)(dcypb)}2(μ-Cl)3] (7), formed by deprotonation of the vinylidene ligand in 5·OC6F5 by TlOC6F5. (An alternative representation of 7 as a covalent Ru(μ-Cl)2Tl species is supported by X-ray evidence, at least in the solid state.) Importantly, the deprotonation reaction is reversible, and competing reprotonation of 7 by the phenol coproduct enables re-formation of 5·OC6F5. Nucleophilic attack by the aryloxide anion on the metal center enables complete and irreversible transformation to 6, illustrating the mutual compatibility of the vinylidene and perfluorophenoxide ligands. As expected from the high thermodynamic stability of the Ru2(μ-Cl)3 entity, complexes 5·PF6 and 5·Cl exhibit low activity in ring-opening metathesis polymerization of norbornene. Mononuclear 6, containing four nonlabile ligands cis to the vinylidene moiety, is likewise quite unreactive until activated by protonolysis of aryloxide. Product identities were established by 1H, 13C, and 31P NMR and IR spectroscopy, and (6, 7, 8) X-ray crystallography.